Fine, very fine, and microfine comminution of brittle materials to obtain products having maximum particle sizes of between 100 and 300 .mu.m (fine comminution) or between 10 and 50 .mu.m (very fine comminution) or between 1 and 5 .mu.m (microfine comminution) usually is accomplished by means of ball mills, vibration mills, planetary mills, agitator mills, and high-pressure roller mills. Until the beginning of the century also stamp mills were used for fine comminution of mineral raw materials. Ball mills, vibration mills, and planetary mills are used both for dry and wet milling, while agitator mills and stamp mills are used almost exclusively for wet milling, and high-pressure roller mills for grinding dry and wet material. As a rule, a mill is combined with a classifier to provide for grinding in a circuit, with the ground product being fed to the classifier where it is divided into fine material and coarse material, the latter being recirculated to the mill for renewed grinding. Ball mills, vibration mills, planetary mills, agitator mills, and especially the known stamp mills have a low degree of efficiency so that the specific energy consumption (the energy requirement based on the mill product obtained by comminution) is very high. Energy consumption for fine comminution (100 to 300 .mu.m) ranges from 10 to 40 kWh/t, it is from 50 to 150 kWh/t for very fine comminution (10 to 50 .mu.m) and above 500 kWh/t for microfine comminution (1 to 5 mm). In addition, the mechanical expenditure is high. A substance exhibits brittle behavior if, prior to beginning to crack, a solid particle of it is deformed largely elastically.
It is true, high-pressure roller mills (U.S. Pat. No. 4,357,287) operating with a pressure in the roller nip of at least 50 MPa require little energy, but the yield in terms of very fine product and especially microfine product at pressures which still can be mastered on an industrial scale is relatively low. This results in a high ratio of coarse material recirculated which in turn requires greater structural units as far as mills, classifiers, and conveyor means are concerned, all involving high capital investment. In the case of nigh-pressure roller mills there is an additional difficulty in the case of microfine grinding in that the material to be ground is poorly drawn into the nip between rollers. The peripheral speed of the rollers, therefore, must be reduced and, possibly, the introduction of material into the nip be supported by feed worms in a feed funnel.
It is an advantage of ball mills and stamp mills that the feeding of the material to be ground into the grinding chamber causes no problems and that they are suitable for wet grinding. They are only little affected by foreign matter and, in principle, sturdier than many other comminuting machines. Parts subject to wear are of simple shape and can be exchanged with ease. Stamp mills have a disadvantage in that the throughput per stamp unit is low.
The one-time stressing of material to be ground in a ram press (U.S. Pat. No. 4,357,287) also requires a high circulation ratio and considerable expenditure for machinery. Following compression in the ram press, the compacted material can be loosened first by mechanical action exerted by corresponding tools which rearrange the material if it is to be stressed once again afterwards by compression before being conveyed out of the grinding chamber for disagglomeration of the resulting agglomerates (briquettes).